The proposed research will extend our previous work and confront basic questions regarding the interrelationship between the lipids of the mitochondrial inner membrane and their metabolism and various lipid-associated enzymes involved in oxidative phosphorylaion, and probes the impact of the normal aging process on these relationships. Specifically we will focus on: Lipid Composition of Intracellular Membranes 1. In quantitative terms, how does the lipid content and composition of intracellular membranes respond to aging? 2. Does fatty acid composition and degree of unsaturation change and could this modulate the effect of lipid compositional change? The Transverse (Asymmetric) Distribution of Phospholipid in the Inner Mitochondrial Membrane 1. Does the asymmetric distribution of phospholipids in the inner mitochondrial membrane change as a consequence of aging? The Metabolic Basis for the Aging-Related Decrease in Cardiolipin 1. Is there a relationship between the aging-related decrease in cardiolipin and the activities of the enzymes involved in its synthesis? 2. Does CTP: phosphatidic acid cytidyltransferase contribute to the aging-related decrease in cardiolipin? Lipid-Associated Enzymes of Mitochondrial Respiration 1. Does control of flux through individual reactions of oxidative phosphorylation change during aging? 2. Identification of aging-related properties of adenine nucleotide translocase which conribute to the change in its relative contribution to the control of respiration.